1. Field of the Invention
Exemplary embodiments of the present invention relate to an apparatus and a method for detecting a packet end point in a wireless communication system; and, more particularly, to an apparatus and a method for detecting a packet end point in a wireless communication system using MIMO-OFDM.
2. Description of Related Art
Much research has recently been performed in the high-speed wireless communication system field to improve the data rate and throughput using various advanced technologies in PHY and MAC layers. In the PHY layer, the data rate has been increased using MIMO, multi-band, OFDM, high-order modulation, use of shorter CP, and link control, and reliability of wireless transmission has been improved by applying advanced channel codec technologies such as Viterbi decoder, turbo code, LDPC, and the like.
In the case of MAC layer, the protocol's overhead can be reduced using packet aggregation and block ACK technologies. Such PHY and MAC research has been performed to improve the maximum coverage and maximum throughput, and much more intensive research is in progress for transmission to transceivers at a larger distance and reliable communication therewith.
And research related to existing technologies has mainly been performed to develop algorithms for improving the performance of demodulators and channel decoders so as to improve performance in low Signal-to-Noise Ratio (SNR), as well as to improve the SNR of RF systems and analog circuits. However, such performance improvement requires that a complicated algorithm be applied to the modem, and implement of the complicated algorithm increases the cost and degrades power consumption efficiency. Furthermore, the limit of RF and analog technologies has restricted the improvement of SNR within the boundary of power and cost competiveness, and different attempts have been made in existing systems to reduce such complexity. That is, there is a need for methods for accurate packet detection in such a low-SNR environment.
FIG. 1 illustrates a packet structure of a packet-based wireless system.
Referring to FIG. 1, the signal field includes a Physical Layer Convergence Procedure (PLCP) header, in which the length of the corresponding received packet is encoded, and data conforming to the length is added behind the header and transmitted. Information included in the signal field is very crucial to decoding of a received data packet. Therefore, Binary Phase Shift Keying (BPSK), which is the simplest form of modulation scheme, is used for modulation, and a parity bit is added to the transmitted signal field value, so that the receiver performs parity check and improves reliability.
However, when the input end of the receiver has a channel state of a relatively low SNR, and when the radio environment has a large delay spread, the error probability resulting from channel noise increases due to wireless transmission/reception characteristics, and there is a high probability that the packet length encoded in the signal field will be erroneously decoded. Such erroneous decoding of the packet length in the signal field of a received packet is followed by erroneous determination of the packet end point in the case of a packet-based wireless communication system, as well as by errors regarding the initialization time of the receiver finite state machine. As used herein, the finite state machine generally refers to a device having a memory configured to store past states/signals. Such erroneous initialization time of the receiver finite state machine seriously degrades system performance in the following two aspects:
Firstly, decoding into a length larger than the actual packet length initializes the finite state machine in the middle of the received packet, and thus the packet is dropped. More specifically, if the packet length is decoded shorter, the receiver is initialized, even in the middle of receiving a packet, and tries to receive a new packet. This means that, after the packet is dropped, the receiver continues the steps of carrier sensing, automatic gain control, synchronization, and signal field decoding. This unnecessarily consumes an excessive amount of power until the actual packet end point arrives.
Secondly, if the packet length is decoded larger than the actual packet length, the finite state machine fails to be initialized, even if the packet reception has ended, and fails to receive the next incoming packet. In this case, the longer the erroneously decoded packet is compared with the actual packet length, the more burst packet errors occur, degrading the receiver minimum sensitivity and the system's overall throughput. When it comes to wireless communication system design, the receiver minimum sensitivity is an important performance index determining the coverage, and the throughput is a critical factor of the user capacity. Therefore, there is a need for research for packet detection that can improve receiver minimum sensitivity and throughput.